In the 1700s, it was discovered that spinning a round lead ball that was being used for a bullet would stabilize the bullet and help keep it on a proper trajectory. It was soon common knowledge that a rifle had about three times the accurate range of a smooth bore musket. When the colonists applied this technology to the battlefield it helped win the Revolutionary War.
During and after the Civil War, cartridge rifles were developed that shot elongated bullets. In 1870 Sir Alfred Greenhill created a formula intended to determine the pitch or twist of the rifling necessary to stabilize an elongated bullet. According to the Greenhill formula, the rifling twist for a given bullet should be 150 times the bullet caliber squared, divided by the bullet length. For example, a 308 caliber bullet having a length of 1.30 inches would have a twist of 150 times 0.308 squared divided by 1.30 which equals 10.95 inches twist or one revolution in every 10.95 inches.
The Greenhill formula worked to stabilize the bullets of his day. Almost all rifled barrels world wide still follow Sir Greenhill's formula. However in 1870, almost all bullets were round nosed or flat pointed round nosed for tubular magazines and had a relatively low ballistic coefficient. The muzzle velocities of these black powder cartridges were much lower than those of the cartridges of today. In general, the Greenhill formula maintains stability for low to medium velocity bullets of low ballistic coefficients throughout their entire trajectory. It will also stabilize modern high velocity supersonic bullets of a high ballistic coefficient in the speed realm only above the speed of sound.
However, for long range shooting, the bullets with a low to medium velocity and low ballistic coefficient have several shortcomings. The slow starting velocity means the maximum range is relatively short. At longer ranges, the bullet drop becomes such that the trajectory must be high, resulting in decreased accuracy. The longer time to target can result in greater wind deflection. Lastly, the velocity/energy remaining at long range may be insufficient to accomplish the intended purpose.
Modern smokeless powder rifle cartridges most often propel bullets of high ballistic coefficients at high supersonic speeds. Most high velocity rifles, rifled according to the Greenhill formula, firing high ballistic coefficient bullets lose accuracy as the bullet slows to slightly faster than of the speed of sound. These bullets tumble or change trajectory as the bullet enters the transonic speed realm. Hence, this determines the effective accurate range of the bullet. Further the Greenhill calculated twist makes no provision for the rotational harmonics of a bullet and therefore rifles made by the Greenhill formula do not have the accuracy potential that is possible.
Heretofore, the standard approach to making a rifle accurate for longer ranges was to increase the distance that the bullet will remain supersonic, so as to impact the target in the supersonic speed range. Consequently, many modern cartridges are made to propel very high ballistic coefficient bullets at very high supersonic speeds. For an example the standard U.S. sniper cartridge (7.62×51 mm M118) has a supersonic range of about 900 yards. To get greater supersonic range, the 338 Lapua Magnum is used and the bullets will stay supersonic and accurate to about 1,800 yards. The 50 caliber Browning machine gun cartridge is used in a 32 pound rifle and has demonstrated accuracy to 2,200 to 2,500 yards depending on the bullet used. The recently developed 416 Barrett was specifically designed to keep the bullet supersonic to beyond 2,500 yards.
Overall, the push to extend the supersonic range of bullets has led to larger rifles using larger cartridges firing at higher breach pressures and bullets of extremely high ballistic coefficients for their calibers. Because of this the shooter has been burdened with physically larger and heavier rifles, heavier ammunition and greater recoil. All this combined greatly limits the mobility of the shooter.
Within the parameters of the strength and weight of a firearm, strength of the shooter, propellants available, bullets used, and recoil developed, there is a physical limit to the range a shoulder fired rifle can shoot a bullet in the supersonic realm.
Therefore, there has been a desire for a rifle having very long range accuracy without extremely high power and velocity.